From: "aharpole (Aaron Harpole) via ruby-core" <ruby-core@...>
Date: 2023-05-25T18:55:58+00:00
Subject: [ruby-core:113660] [Ruby master Feature#19694] Add Regexp#timeout= setter

Issue #19694 has been reported by aharpole (Aaron Harpole).

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Feature #19694: Add Regexp#timeout= setter
https://bugs.ruby-lang.org/issues/19694

* Author: aharpole (Aaron Harpole)
* Status: Open
* Priority: Normal
----------------------------------------
# Abstract

In addition to allowing for a Regexp timeout to be set on individual instances by setting a `timeout` argument in `Regexp.new`, I'm proposing that we also allow setting the timeout on Regexp objects with a `#timeout=` setter.

# Background

To be able to roll out a global Regexp timeout for a large application, there are inevitably some individual regexes for which a different timeout is appropriate. While the `timeout` keyword argument was added to `Regexp.new`, this isn't always a viable option.

In the case of regex literal syntax (`/ab*/` or `%r{ab*}`, for instance), it's not possible to set a timeout at all right now without converting to `Regexp.new`, which may be awkward depending on the contents of the regex.

It also is desirable from time to time to be able to set a timeout for a regex object after it's been initialized.

Finally, because we offer a `Regexp#timeout` getter, for consistency it would be nice to also offer a setter.

The introduction of a `Regexp#timeout=` setter was mentioned as a possible way to set individual timeouts in https://bugs.ruby-lang.org/issues/19104#Specification.

# Proposal

I propose that we add the method `Regexp#timeout=`. It works the same way the `timeout` argument works in `Regexp.new`, taking either a float or nil.

This makes it relatively easy to add timeouts to specific regex literals (regex literals are frozen by default so you do have to `dup` them first):

```
emoji_filter_pattern = %r{
  (?<!#{Regexp.quote(ZERO_WIDTH_JOINER)})
  #{EmojiFilter.unicodes_pattern}
  (?!#{Regexp.union(EmojiFilter::MODIFIER_CHAR_MAP.keys.map { |k| Regexp.quote k })})
}x.dup
emoji_filter_pattern.timeout = 1.0
emoji_filter_pattern.freeze
```

# Implementation

This setter has been implemented in https://github.com/ruby/ruby/pull/7847.

# Evaluation

It's just a setter, so pretty straightforward in terms of implementation and use.

# Discussion

It's worth considering other options for overriding `Regexp.timeout`. I'd love to see something like the following for overriding regexp timeouts as well:

```
Regexp.timeout = 1.0

Regexp.with_timeout(5.0) do
  evaluate_slower_regexes
end
```

It's possible to implement something like `Regexp.with_timeout` but it's not thread-safe by default since it would involve overwriting `Regexp.timeout`.

# Summary

Regexp instances have a getter for timeout, and adding a corresponding setter adds consistency and will make it easier for developers to adopt adding a global `Regexp.timeout` by making it simpler to adjust timeouts on a regex by regex basis.

It's a minor change but the added consistency and flexibility help us optimize for developer happiness.



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